1. Field of the Invention
The present invention relates to a method of and and apparatus for coating paint to the inner and outer surfaces of joined areas of can barrels which are produced by a can barrel forming device.
2. Description of Background Art
Heretofore, the joined areas of a welded can for use as a can container are covered with protective paint coat layers in order to prevent the metal material of the can from being eluted into the canned substance and to prevent the joined areas from being eroded by the canned substance and to or by atmosphere with time. Such protective paint layers can be coated by applying liquid paint or powdery paint. The use of liquid paint is more advantageous since it can be more easily applied, it can produce a better coating appearance and it is more reliable in protecting the joined areas. The liquid paint is usually applied by flow coating or spray coating.
One known apparatus for applying liquid paint through spray nozzles to the inner and outer surfaces of joined areas of a can barrel produced by a can barrel forming device is illustrated in FIG. 4 of the accompanying drawings. The can barrel forming device, denoted at forms a square-shaped blank X' into a tubular form with its opposite edges joined by seam welding to provide a can barrel X of uniform diameter, which is then intermittently fed along an arm in the axial direction of the can barrel. The can barrel X is fed by a conveyor device c with the joined area Y held upwardly. A plurality of such can barrels X are successively fed by the conveyor device c in spaced-apart relationship. The opposite surfaces of the joined area Y of the can barrel X are coated with paint by a coating device f having a first spray nozzle which applies liquid paint, from below, to the inner surface of the joined area Y and a second spray nozzle which applies liquid paint, from above, to the upper surface of the joined area Y.
While the liquid paint is being continuously ejected toward the inner and outer surfaces of the joined area Y from the first and second spray nozzles d, e located inside and outside of the can barrel X which is fed at a relatively high speed, a mist of liquid paint is scattered through a gap h between adjacent can barrels X. This mist of liquid paint tends to contaminate the working environment and surrounding devices, and to smear portions of the can barrel other than the joined area. One solution would be to eject the liquid paint intermittently so that the liquid paint would be applied only to can barrels X and would not be ejected into gaps between adjacent can barrels X. It would additionally be desirable to apply a paint coating of uniform thickness to each of the opposite ends of the joined area Y of a can barrel X. However, such a coating process would require a sophisticated control system.